Looking around, it seems this problem is common, and just as common is the buck passing to and fro between merchant and bank with neither wanting to help the customer. ONLY if a fault is identified with how the bank dealt with the matter would a complaint about the bank be upheld. If the problem is held to be with the retailer or their acquirer, then this would be the subject of a separate complaint, possibly one of not being treated fairly.
Above all, it seems it's only a real problem when DEBIT cards are used, because any errors such as this can prevent people from accessing their own money, including paying bills. Use a CREDIT card though, and unless you are running it uncomfortably close to the limit (which you shouldn't routinely be doing), then this type of error will remove a part from the top of your credit limit, and this should not ordinarily cause inconvenience during the time it takes to resolve itself.
Here is an example of someone getting the runaroud between Mothercare and their bank in much the same way as this case, until the matter eventually resolved itself after 7 days.
One contributor even mentioned the solution:-
Contact mothercare and ask them to fax your bank saying they wont be collecting it along with the payment details and your bank should lift the ringfence on the funds.
However, even with no action being taken, the charge should either be taken or drop after a few days, expressed as "working days", so would not include weekends and bank holidays. For debit cards, this should be around 5 working days, so a calendar week.
Ask the bank for it's policy on "authorisation holds", and for how long such holds are applied where the merchant does not collect the money before they drop automatically. Unless this period was exceeded, then it's probably not really down to the bank, it's Redbet that should have acted, specifically, they should have cancelled the authorisation hold from their end once they had decided they would not be actioning the charge. However, if the time was exceeded, then something else happened that caused the bank to stray from it's usual policy, which might be cause for complaint.
There is something rather worrying though, it seems that consumers have little protection and few rights of immediate redress when such problems occur. Often the problem is made worse by merchants asking the customer to "try again", as this can create duplication of authorisation holds, and even duplicate charges being made. I remember having a rant about MGS banking saying "please try again" when my Neteller deposits were supposedly "declined", only to find that they had been debited, and that by following this advice I had double the mess to clean up when I had TWO declines, but also TWO deposits taken from my Neteller.
I think this is a serious weakness in electronic money transfer systems, and as such, consumers should have more rights in regard to getting something done, and a clear definition of who is to do this rather than the current stalemate where the merchant and bank both blame each other.
In the mean time, it seems that using a credit card affords much more protection as it's not your money stuck in limbo, it's the bank's money (It has agreed to lend you the amount of the purchase, has set it aside, but has not yet actually lent it to you), and unless the charge is subsequently processed, you do not pay a pending charge on your credit card statement, nor is interest charged even if it sits pending "forever".
An alternative is to have a separate account purely for debit card gambling, so that if an error holds some of your gambling budget in limbo, it just prevents the casino industry making that amount from you that week, but has no impact on your non gambling bank account activity, so everything else you do should not be impacted.
If you are panicking because today is 100% bonus day, remember that there will be another coming along, and in many cases it can be predictable.